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Subject: Re: [PATCH v2 1/2] ARM: Fix some check warnings of tool sparse
To:     Ard Biesheuvel <ardb@kernel.org>
CC:     Russell King <linux@armlinux.org.uk>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
References: <20221010095346.1957-1-thunder.leizhen@huawei.com>
 <20221010095346.1957-2-thunder.leizhen@huawei.com>
 <CAMj1kXHOv23JY35fZ45k=Pzi=ROd6BOCxqPkfXLh2520qhoFzQ@mail.gmail.com>
 <1ab4c651-f0ab-1107-1784-ad255dabc33a@huawei.com>
 <CAMj1kXHn70rRaB=BgCrMoqQxRcq=HzZ0NWFYL+FqV_037PaY3w@mail.gmail.com>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Message-ID: <c262c991-ad1e-81e6-4909-b8c4a1c036ff@huawei.com>
Date:   Tue, 11 Oct 2022 10:29:58 +0800
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On 2022/10/10 19:06, Ard Biesheuvel wrote:
> On Mon, 10 Oct 2022 at 12:58, Leizhen (ThunderTown)
> <thunder.leizhen@huawei.com> wrote:
>>
>>
>>
>> On 2022/10/10 18:20, Ard Biesheuvel wrote:
>>> On Mon, 10 Oct 2022 at 11:56, Zhen Lei <thunder.leizhen@huawei.com> wrote:
>>>>
>>>> Fix the following warnings:
>>>>  warning: incorrect type in initializer (different address spaces)
>>>>     expected unsigned short [noderef] __user *register __p
>>>>     got unsigned short [usertype] *
>>>>  warning: cast removes address space '__user' of expression
>>>>
>>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
>>>> ---
>>>>  arch/arm/kernel/traps.c | 10 +++++-----
>>>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
>>>> index 20b2db6dcd1ced7..34aa80c09c508c1 100644
>>>> --- a/arch/arm/kernel/traps.c
>>>> +++ b/arch/arm/kernel/traps.c
>>>> @@ -188,9 +188,9 @@ static void dump_instr(const char *lvl, struct pt_regs *regs)
>>>>                         }
>>>>                 } else {
>>>>                         if (thumb)
>>>> -                               bad = get_user(val, &((u16 *)addr)[i]);
>>>> +                               bad = get_user(val, &((u16 __user *)addr)[i]);
>>>>                         else
>>>> -                               bad = get_user(val, &((u32 *)addr)[i]);
>>>> +                               bad = get_user(val, &((u32 __user *)addr)[i]);
>>>>                 }
>>>>
>>>>                 if (!bad)
>>>> @@ -455,15 +455,15 @@ asmlinkage void do_undefinstr(struct pt_regs *regs)
>>>>         if (processor_mode(regs) == SVC_MODE) {
>>>>  #ifdef CONFIG_THUMB2_KERNEL
>>>>                 if (thumb_mode(regs)) {
>>>> -                       instr = __mem_to_opcode_thumb16(((u16 *)pc)[0]);
>>>> +                       instr = __mem_to_opcode_thumb16(((__force u16 *)pc)[0]);
>>>
>>> Shouldn't this be __user as well? (and below)
>>
>> unsigned int instr;
>> void __user *pc;
>>
>> The __user can clear the warning, but a new warning will be generated.
>>
>> instr = __mem_to_opcode_thumb16(((u16 *)pc)[0]);
>>       ^new                           ^old
>>
>> arch/arm/kernel/traps.c:473:33: warning: dereference of noderef expression
>>
> 
> This is because dereferencing a __user pointer is not permitted.
> 
> So this code should be using get_kernel_nofault() here not a plain
> dereference of PC. So better to fix that properly instead of papering
> over it with a __force cast just to make sparse happy.

How about:
@@ -451,9 +451,9 @@ int call_undef_hook(struct pt_regs *regs, unsigned int instr)
 asmlinkage void do_undefinstr(struct pt_regs *regs)
 {
        unsigned int instr;
-       void __user *pc;
+       void *pc;

-       pc = (void __user *)instruction_pointer(regs);
+       pc = (void *)instruction_pointer(regs);

        if (processor_mode(regs) == SVC_MODE) {
 #ifdef CONFIG_THUMB2_KERNEL
@@ -497,7 +497,7 @@ asmlinkage void do_undefinstr(struct pt_regs *regs)
        }
 #endif
        arm_notify_die("Oops - undefined instruction", regs,
-                      SIGILL, ILL_ILLOPC, pc, 0, 6);
+                      SIGILL, ILL_ILLOPC, (void __user *)pc, 0, 6);
 }
 NOKPROBE_SYMBOL(do_undefinstr)


The 'pc' may come from kernel or user. And I found that all the get_user()
calls have already done type casts to the pc, except arm_notify_die().
I think the above changes are reasonable.

> 
> 
>>>
>>>>                         if (is_wide_instruction(instr)) {
>>>>                                 u16 inst2;
>>>> -                               inst2 = __mem_to_opcode_thumb16(((u16 *)pc)[1]);
>>>> +                               inst2 = __mem_to_opcode_thumb16(((__force u16 *)pc)[1]);
>>>>                                 instr = __opcode_thumb32_compose(instr, inst2);
>>>>                         }
>>>>                 } else
>>>>  #endif
>>>> -                       instr = __mem_to_opcode_arm(*(u32 *) pc);
>>>> +                       instr = __mem_to_opcode_arm(*(__force u32 *) pc);
>>>>         } else if (thumb_mode(regs)) {
>>>>                 if (get_user(instr, (u16 __user *)pc))
>>>>                         goto die_sig;
>>>> --
>>>> 2.25.1
>>>>
>>>>
>>>> _______________________________________________
>>>> linux-arm-kernel mailing list
>>>> linux-arm-kernel@lists.infradead.org
>>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>> .
>>>
>>
>> --
>> Regards,
>>   Zhen Lei
> .
> 

-- 
Regards,
  Zhen Lei